CIE 51.2

A method is provided for evaluating the suitability of a test source as a simulator of CIE Standard Illuminant D55, D65, or D75. For each of these three Standard Illuminants, spectral radiance factor data are supplied for five pairs of non-fluorescent samples that are metameric matches. The colorimetric differences of the five pairs are computed for the test illuminant; the average of these differences is taken as the Visible Range Metamerism Index, and this is used as a measure of the quality of the test illuminant as a simulator for non-fluorescent samples. For fluorescent samples, the quality is further assessed in terms of an Ultraviolet Range Metamerism Index; this consists of the average of the colorimetric differences computed with the test illuminant for three further pairs of samples, each pair consisting of a fluorescent and a non-fluorescent sample, which are metameric under the Standard Illuminant.